1. Field of the Invention
The present invention relates to methods and apparatus for improved safety for end treatments on roadway guardrails. In particular, the present invention features an improvement upon the guardrail extruder terminal safety device.
2. Description of Related Art
Guardrails present a unique fixed object safety problem due to the raised ends which they sometimes present. Therefore, a number of guardrail end treatments have been developed which attempt to reduce the hazard presented by the raised ends. Guardrail end treatments seek to reduce the harmful effects of collisions with the ends of guardrails by absorbing, redirecting or cushioning impacts with the end of the rail. One popular end treatment is the guardrail extruder terminal, which is currently marketed commercially under the trade name ET-2000. The guardrail extruder terminal serves to attenuate impacts with the end of the guardrail and provides anchorage for impacts to the sides of the guardrail. In an end-on impact, the guardrail extruder terminal progressively flattens the beam of the guardrail and bends the flattened member in a curvilinear arc in a direction away from the colliding vehicle. Aspects of the guardrail extruder terminal have been described and claimed in U.S. Pat. No. 4,928,928, entitled "Guardrail Extruder Terminal," issued to Buth et al. on May 29, 1990, and U.S. Pat. No. 5,078,366, also entitled "Guardrail Extruder Terminal," issued to Sicking et al. on Jan. 7, 1992. Both of these patents have been assigned to the assignee of the present invention and are incorporated herein by reference. The ET-2000 is available commercially from Trinity Industries in Dallas, Tex. The guardrail extruder terminal features a generally vertically-oriented, rectangular striking plate or impact plate which will contact and engage an impacting vehicle. Normally, this plate is covered with a reflective material so that it is visible to an approaching vehicle.
As originally developed, the guardrail extruder terminal is constructed so that the lower edge of the front striking plate is located approximately 10-12" above the ground or roadway surface. At this height, however, the impact head may contact and engage a smaller impacting vehicle above its chassis or structural frame when impacted by this side of the vehicle. As a result, a smaller vehicle's superstructure can sustain damage from the impact head. Further, there is a risk that smaller vehicles having side door openings which are larger than the impact head may have the door punched through or punched out by the head during a collision in which the side of the vehicle impacts the head. A smaller car may even tend to wedge itself beneath the impact head in some situations, thus reducing or eliminating the advantage provided by the impact head in preventing penetration. This may occur, for example, if the guardrail extruder terminal is mounted toward the top of a convex slope, thereby leaving the lower edge of the head somewhat higher than is normal or desired for the terminal.